112 



THE AMERICAN MONTHLY 



[June, 



out immersion, we will find ourselves 

 in the domain of the bacteria, in the 

 situation of the traveller who wanders 

 in an unknown country at the hour of 

 twilight, at the moment when the light 

 of day no longer suffices to enable him 

 clearly to distinguish objects, and 

 when he is conscious that, notwith- 

 standing all his precautions, he is 

 liable to lose his way." 



Among the Cyanophyceae, the Nos- 

 tocaceae possess vibratile cilia, covering 

 those peculiar cells, called connecting 

 cells or Heterocysts. The plants of 

 this family are moniliform rows of 

 cells, usually simple, though some- 

 times branched. These threads are 

 free or inclosed in gelatinous sheaths, 

 the greater number of cells are green 

 and capable of division, but between 

 them occur, at greater or less distances, 

 or at the ends of the threads, colorless 

 ciliated cells of considerable size, and 

 incapable of division — the hetero- 

 cysts. Individual cells without any 

 apparent law may becom.e heterocysts. 

 They have been supposed to repre- 

 sent the antheridia of the higher or- 

 ders of cryptogams. Passing from the 

 Protophyta we find the next higher 

 class of plants, viz., the Zygosporese, 

 exhibiting some interesting instances 

 of vibratile cilia. Here we find the 

 Volvocineae, the conjugating cells of 

 which are locomotive, and which are, 

 during their vegetative period, con- 

 tinually in motion, interrupted only by 

 certain periods of repose ; the motion, 

 as is usual with swarm-spores, being 

 caused by two cilia. They are, how- 

 ever, distinguished from swarm-spores 

 by the cells, which either live isolated 

 (Protococcus and Chlamydococcus), or 

 unite into angular and tabular (Goni- 

 um) or spherical families (Volvox 

 Stephanosphoera Pandorina), being 

 surrounded while in motion by a 

 membrane through which the cilia 

 project into the water, and produce 

 by their vibrations the rotary progres- 

 sive movement of the single cell, or 

 the whole family. The Volvox glob- 

 ator, so common an object at micro- 

 scopical exhibitions, is, perhaps, the 



best member of this group for the 

 student of ciliary movement to ex- 

 amine. 



Right here we come to that little 

 unicellular plant, Protococcus, the clas- 

 sification of which is in dispute. While 

 this reproduces mostly by fission, it at 

 times, after a period of rest, gives 

 forth by internal cell-division, a mo- 

 tile form, provided with two cilia. 

 This is the one most used for the 

 demonstration of vibratile cilia in 

 plants, since it is easily found, the 

 cilia becoming distinctly visible as the 

 plant approaches death, and the move- 

 ments, for that reason, become less 

 rapid. In this brief consideration of 

 the leading examples of vibratile cilia 

 in plants, we have seen, that as a rule, 

 the period during which the cilia live 

 and vibrate is short, existing in a few 

 instances only, in adult plant life. Of 

 the correspondence between the vibra- 

 tile filaments of plants and those of 

 animals, we have already spoken 

 briefly ; but we have every reason to 

 believe that similar molecular particles 

 produce ciliary motion in the vegeta- 

 ble kingdom as well as in the animal. 



Rationale and Function of Cil- 

 iary Motion. — Regarding the cause 

 of ciliary movement, a variety of opin- 

 ions have been put forward. Ehren- 

 berg claimed that "each cilium was 

 furnished with a bulb at the root, to 

 which minute muscles were attached," 

 a slight degree of rotation, communi- 

 cated to the bulb, causing a much 

 more extensive motion to the rest of 

 the organ, 



Valentin, Buhlmann, Friedreich, 

 Eberth and others assert that the 

 movements are dependent upon the 

 contraction of the protoplasm in which 

 the roots of the cilia arise. Klein 

 and Prudden claim the movements 

 are due to the contraction of introcel- 

 lular reticular fibres ; thus, the former 

 says : " Supposing the introcellular 

 net-work contracts to one side in a 

 horizontal diameter, each such con- 

 traction acts naturally on the lower 

 ends of the cilia, whereby they are 

 pulled to the same side, while the 



